Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $104.48   13.648%   $118.7394   $118.74   $118.75   $118.70  
  Purchase #2 $156.59   6.490%   $166.7527   $166.75   $166.75   $166.80  
  Purchase #3 $40.49   12.717%   $45.6391   $45.64   $45.65   $45.60  
  Purchase #4 $167.35   6.186%   $177.7023   $177.70   $177.70   $177.70  
  Purchase #5 $93.55   6.331%   $99.4727   $99.47   $99.45   $99.50  
  Purchase #6 $77.79   10.778%   $86.1742   $86.17   $86.15   $86.20  
  Purchase #7 $67.26   7.226%   $72.1202   $72.12   $72.10   $72.10  
  7 purchase totals = $707.51       $766.6006   $766.59   $766.55   $766.60